In the field of exercise devices, inventors have developed devices for use in exercising a user's abdominal and other core muscles. Inventors have employed various devices that allow the user to exercise the abdominal and other core muscles through relative motion of the user's upper body and lower body, including bending motions and twisting motions.
Of the mechanisms used to allow exercise by a twisting motion, some mechanisms provide a rotating base on which the user may stand and twist the upper body and lower body relative to each other from side to side. Some such mechanisms provide fixed handles that may be gripped by the user while standing on a rotating base, as disclosed in U.S. Pat. No. 7,118,519 to Slowinski, U.S. Pat. No. 4,305,579 to Rice, and U.S. Pat. No. 5,433,690 to Gilman. A contrary approach is disclosed in U.S. Pat. No. 4,249,727 to Dehan, which discloses a mechanism in which the user stands on a fixed base and moves a bar mounted to the base in a ball-and-socket fitting so as to provide resistance against the user when the user attempts to move the bar. In addition, an exercise device has been sold consisting of a rotatable base on which the user may stand and rotate the user's upper body relative to the upper body, but with no handle or bar for gripping by the user.